Andrew Wilson : Mail::Address::Tagged.pm

"This module implements an object that can generate and validate tagged email addresses. These are designed to be used primarily in anti-spam applications.
The addresses generated all carry extra information, such as the date when they expire, who may use them to send you mail etc. A cryptocraphic hash of this extra information is also included in in the address. This Hashed Message Authenticaion Code (HMAC RFC 2104) is your guarantee that the information contained in the address has not been tampered with."